FORT MYERS, Fla. — As his Red Sox teammates were taking batting practice inside JetBlue Park Tuesday morning, right fielder Shane Victorino was walking out the clubhouse door with physical therapist Dan Dyrek to do some work on one of the back fields.

The Red Sox have had six full-squad workouts since opening spring training and Victorino has been a part-time participant as he recovers from surgery on his right thumb.

On Tuesday, manager John Farrell revealed that there is a second physical issue.

“He went through two really good days of work,” said Farrell. “Coming out of swinging the bat off the tee, soft toss, and some light BP, we felt there were some other things we needed to address just from core strengthening and he’s going through that right now.”

Victorino had groin problems last season and the Red Sox are using some time in spring training to prepare him for the season.

“This is not related to the hand,” Farrell said. “He feels good there. He came out and ran today for about 12 minutes, ran the bases some. He threw. We just feel there’s more to his base and foundation that we can build physically before ramping up the work.”

Farrell did not have a date for Victorino to get in games, saying the core work has to be taken care of first. The issue is not expected to affect Victorino’s availability for Opening Day. If he is able to play in a week or two, there would be plenty of exhibition games remaining.

Surprising Sizemore

Outfielder Grady Sizemore is progressing quicker than the Red Sox expected, given the two years he missed with various injuries.

“We came into camp knowing we were going to have to work off of his readiness and comfort level,” Farrell said. “He’s answered everything within the schedule so far. You can see the look on his face and the way he answers questions about fundamentally the timing at the plate or physically how he’s responding.”

Sizemore is scheduled to play Thursday in the doubleheader against Northeastern and Boston College.

“Definitely better than expected,” he said. “I didn’t expect to come in here and have continuous days without any issues and be able to keep pushing it to keep up with the volume and keep going from there.”

In the first days of camp, Sizemore wondered whether he would be ready for the early games. But those concerns have vanished for now.

“Thursday is not too soon based on some of the answers he’s gotten through the workouts,” Farrell said.

Farrell said there is less checking in with Sizemore on a daily basis than was expected.

“The doubt is less,” the manager said. “Based on what he has been able to do so far, those pressing questions are a little less than first anticipated.”

Sizemore is competing for a spot in what could become a crowded outfield. A center fielder throughout his career with the Indians, Sizemore has been taking balls in left and center with the Red Sox.

Depth at closer

The Red Sox, cognizant of what transpired last season, have stacked up potential closers behind Koji Uehara. Farrell said Edward Mujica and Andrew Miller would be the primary options on days Uehara needs a rest. Mujica had 37 saves for the Cardinals last season and has 41 in his career. Miller does not have a save in his career but averaged 14.1 strikeouts per nine innings last season. Junichi Tazawa, who has one save in his career, is another possibility . . . Daniel Nava has been cleared to resume batting practice Wednesday. He did not swing a bat for four days because of a pinched nerve in his neck. Nava will not play in either of the games Thursday.